The diagram below shows the formation of a volcanic arc as a result of an oceanic plate moving underneath a continental plate at a subduction zone. When volcanoes erupt, magma (hot, molten rock) rises toward the surface of the Earth. As magma cools, solid rock forms. This rock contains substances from the interior of the Earth. Which of the following natural resources is likely to be plentiful near subduction zones where volcanic activity has occurred in the past?